1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying apparatus, a printer or the like, and more particularly to an apparatus employing fixing means provided with a rotating member heated by induction heating.
2. Related Background Art
The image forming apparatus based on the electrophotographic process is provided with a fixing device for fusion fixing toner to a transfer material, by applying heat and pressure while sandwiching and conveying the transfer material and the toner, borne on the transfer material and composed of a resinous material, a magnetic material, a coloring material etc. in a pressure contact portion (nip portion) of a fixing roller and a pressure roller maintained in mutual pressurized contact and in rotation.
In such fixing device, there is proposed, as heating means, a method of generating an eddy current in an electroconductive layer provided on the fixing roller by means of a magnetizing coil thereby generating Joule heat. The method allows to position the heat source very close to the toner, thereby being featured in shortening the time required by the surface temperature of the fixing roller to reach a temperature adequate for fixing at the start-up of the fixing device, in comparison with the conventional heat roller system employing a halogen lamp. It is also featured by a high heat efficiency because of the short and simple heat transmission path from the heat source to the toner.
In such fixing device to the induction heating type, it is preferable to heat the fixing roller in the stand-by state in order to further expedite the starting of the device, but the rotation of the fixing roller in such state is not desirable in consideration of the heat efficiency because such rotation induces wasted heat radiation from the fixing roller constituting the heat source.
An object of the present invention is to provide an image forming apparatus capable of efficiently warming the rotating member of the fixing means.
Another object of the present invention is to provide an image forming apparatus provided with unfixed image forming means for forming an unfixed image based on an image formation start signal, and fixing means for fixing the unfixed image formed by the unfixed image forming means on a recording material, wherein the fixing means includes a rotating member and a magnetic flux generating means for generating a magnetic flux by supplying power, wherein the magnetic flux generated by the magnetic flux generating means generates an eddy current in the rotating member, so that the rotating member generates heat by the eddy current, thereby an image on the recording material is heated, and wherein, in a stand-by state prior to an input of the image formation start signal, the rotating member stops rotation and the magnetic flux generating means is energized.
Still other objects of the present invention, and the features thereof, will become fully apparent from the following description.